The present invention relates generally to a biometric data acquisition assembly, and more particularly to a body fat analyzer having measurement electrodes made from a conductive film integrated on a substrate. It further relates to a water-resistant body fat analyzer having electrodes mounted on its upper surface and connected to measurement circuits within the analyzer without requiring perforations in its upper surface.
Percent body fat has long been recognized as a useful indicator of a person""s health. One technique that has been developed to measure a person""s percent body fat is the so-called xe2x80x9cbioelectrical impedancexe2x80x9d technique. According to this technique, a person""s body fat is measured by determining the impedance of the person""s body to electrical signals, and calculating the percent body fat based upon the measured impedance and other variables such as height, weight, age, and sex. Body impedance is typically determined by supplying a constant current through at least two electrodes that contact the body, thereby causing a voltage to develop across the body. This voltage is measured either (1) via the same electrodes through which current is supplied, or (2) via one or more pairs of voltage-measuring electrodes. The body impedance is then readily calculated from the current and the measured voltage, and the percent body fat is in turn calculated from the body impedance.
Although many body fat analyzers based on these techniques are currently available in the retail market, they tend to have bulky electrodes, to be susceptible to damage from water, and to be relatively expensive to manufacture. One example of such a body fat analyzer is described in U.S. Pat. No. 5,611,351 and shown in FIG. 1. With reference to FIG. 1, a user stands on four large metal electrodes 2,3, through which current is supplied and the developed voltage measured. The user""s weight and height are also measured, by a weight scale within base 5 and height scale 4,4A. The user""s body impedance and body fat are then calculated and displayed on display 6. A plan view of base 5 is shown in FIG. 2, and a sectional view is shown in FIG. 3. From these figures, it may be seen that electrodes 2,3 are large, thick, and bulky. Such electrodes are relatively expensive to manufacture, since they require a large amount of raw material and processing. Further from FIGS. 1-3, although the wiring associated with electrodes 2,3 is not directly indicated, they appear to be connected to the measurement and display circuitry 6 via conductors that pass through openings in the upper surface 1 of base 5. These openings may disadvantageously permit water and dust to enter base 5. Moreover, despite the size of electrodes 2,3, the user is required, by their geometry and by heel guides 7, to place his feet in very specific locations, which may not be comfortable for users of different body types. Finally, since electrodes 2,3 alone support the user""s weight, he may feel some discomfort as the electrodes press into his feet.
A more recent bioimpedance body fat analyzer, described in U.S. Pat. No. 6,308,096 and shown in FIGS. 4 and 5, comprises a handheld unit 40 and a base unit 42, connected by a cord 44. The analyzer has eight electrodes, four in handheld unit 40 and four in base unit 42. It may be seen from FIG. 5 that the base-mounted electrodes 50, 52 in this body fat analyzer are relatively small, and flush-mounted in a rubber support 54, itself mounted on a base 56 and held in position by upper layer 58. Although this body fat analyzer is more comfortable to use than that described above, it is still relatively expensive to manufacture because of the large number of manufacturing steps required to mold electrodes 50, 52, mount them in rubber support 54 and then install the assembly in position between base 56 and upper layer 58.
Still another recent body fat analyzer is described in U.S. Pat. No. 6,243,651 and shown in FIGS. 6 and 7. This analyzer is less expensive to produce than those described above, since it is a small, handheld unit having a compact plastic case 60 and four small electrodes 62. Electrodes 62 are made of stainless steel (SUS) sheet metal, which can be produced and installed more easily than the molded electrodes in the analyzers described above. But this analyzer, too, requires manual assembly and thus is still relatively expensive to produce. Additionally, like the analyzers described above, this analyzer is susceptible to damage by moisture that may reach the inside of the unit through openings in the case 60 around the keys 64, display 66, or at the points at which electrodes 62 (or their associated conductors) enter case 60.
It is therefore an object of the present invention to provide a body fat analyzer having a reduced risk of damage by environmental factors.
It is a still further object of the present invention to provide a body fat analyzer that may be easily and inexpensively mass-produced.
The inventor of the present invention has accomplished these objectives through the application of conductive-film integration technology to body fat analyzers. Thus, a body fat analyzer in accordance with the invention preferably comprises a substrate; at least two conductive-film electrodes integrated on the substrate and capable of contacting a body to be measured; and a body fat measurement circuit electrically connected to the electrodes.
A problem that arises when such an analyzer is constructed is that conductive-film electrodes have high resistances, e.g., between 1-100 ohms, which affects the measured value of resistance. In accordance with the present invention, this problem is overcome by configuring the body fat measurement circuit to calculate, based upon the measured body impedance, a corrected body impedance value that is independent of the impedance of the electrodes.
The substrate may be composed of any non-conductive material capable of receiving a conductive-film layer. Suitable materials include, e.g., glass, ceramics, plastics, non-conductive stones, and insulators.
The electrodes may be composed of any conductive material suited to application as a conductive film on a substrate, e.g., metals, semiconductors, conductive inks and pastes, and transparent conductive materials such as zinc stannate (ZnSnO3 and Zn2SnO4), fluorine-doped zinc oxide (ZnO:F), indium tin oxide (In2O:Sn and In2O3:Sn), titanium nitride (TiNx), and fluorine-doped tin oxide (SnO2:F). In order to minimize material and processing costs while maintaining a suitable conductance, the electrodes are preferably between 20 nanometers to 5 micrometers thick.
Preferably, a body fat analyzer in accordance with the invention further comprises a heating element in contact with the substrate and capable of warming the surface of the analyzer. This warming action renders the analyzer more comfortable to use and may also increase the accuracy of the body fat measurement, since better capillary blood flow at the surface of the foot results. To control the heating element, a current source electrically connected to it is also required. Still more preferably, since the conductive-film electrodes themselves have a relatively high resistance, they may be used as the heating elements, and the current source may be included in the body fat measurement circuit.
In a further embodiment of the present invention, other circuits useful in body fat analyzers may be additionally provided on the substrate as integrated circuits. Such circuits may include, for example, a thin-panel display, a touch-switch keypad, and an electromagnetic shield positioned to protect the measurement circuit. Preferably, the measurement circuit itself is integrated on or under the substrate.
The present invention further includes a method of producing a body fat analyzer, comprising the steps of: (1) forming two or more conductive-film electrodes on a substrate; and (2) electrically connecting a biometric data acquisition circuit to the electrodes. The electrodes may be formed on the substrate by known thin- or thick-film integration techniques, such as sputtering, vapor deposition, photolithography, screen-printing, etc.
The electrodes may be shaped by either of two known techniques: (1) creating a uniform layer of conductive material on the substrate; and selectively removing predetermined portions of the conductive material by, e.g., chemically etching, sand-blasting, laser patterning, or grinding away predetermined portions of the conductive material; or (2) by applying the electrode material only to selected portions of the substrate. Preferably, the method of producing the body fat analyzer further comprises the step of additionally integrating, on the substrate, at least one of (1) a thin-panel display, (2) a touch-switch keypad, (3) a heater element, and (4) an electromagnetic shield.
In another embodiment of the invention, a body fat analyzer having improved water-resistance is provided. It comprises a substrate having top and bottom surfaces and an edge therebetween; at least two electrodes in contact with the top surface of the substrate, and capable of contacting an object having a biometric electrical characteristic to be measured; and a body fat measurement circuit mounted below the substrate and electrically connected to the electrodes such that the top surface of the substrate remains intact, whereby water present thereon is prevented from reaching the circuit. Preferably, the circuit is located below the bottom surface of the substrate and is connected to each of the electrodes via a conductive path traversing the edge of the substrate. To further improve the water-resistance of the analyzer, a gasket is preferably mounted on the substrate that tends to keep water present on the top surface of the substrate from reaching the bottom surface of the substrate.
The invention, in this embodiment, further includes a method of producing a body fat analyzer, comprising the steps of: (1) affixing at least two electrodes on the top surface of a substrate having top and bottom surfaces and an edge therebetween; and (2) electrically connecting the electrodes to a biometric data acquisition circuit mounted below the substrate, such that the top surface of the substrate remains intact, whereby water present thereon is prevented from reaching the circuit. Preferably, the connecting step includes the step of providing, for each electrode, a conductive path from the electrode on the substrate""s top surface to its bottom surface via its edge. Finally, the method preferably includes the step of providing, near the edge of the substrate, a gasket that tends to keep water present on the top surface of the substrate from reaching the bottom surface of the substrate.